A recent review paper by the US Geological Survey suggests that the arctic could potentially alter the Earth’s climate by becoming a source of global atmospheric carbon dioxide.
In the new review, David McGuire of the U.S. Geological Survey and the University of Alaska at Fairbanks, along with his colleagues, shows that the Arctic has been a carbon sink since the end of the last Ice Age. In recent times this has accounted for between zero and 25 percent, or up to about 800 million metric tons, of the global carbon sink.
According to the report, the Arctic accounts for an average 10-15 percent of the Earth’s carbon sink. The worry is that the rapid rate of climate change in the Arctic could alter, or indeed eliminate the sink, which in turn could make the Arctic a source of carbon dioxide instead.
Carbon generally enters the oceans and land masses of the Arctic from the atmosphere and accumulates in permafrost. Unlike active soils, permafrost does not decompose its carbon; thus, the carbon becomes trapped in the frozen soil.
The concern is that recent warming trends could change the balance between accumulation and release of carbon in the arctic permafrost. Warmer temperatures accelerate the rate of surface organic matter decomposition,in turn releasing more carbon dioxide into the atmosphere.
“In the short term, warming temperatures could release more Arctic carbon to the atmosphere,” says McGuire. “And with permafrost thawing, there will be more available carbon to release.”
McGuire says that thawing permafrost could also result in a more waterlogged Arctic, and this could encourage the activity of methane-producing organisms. As it stands, the Arctic is a substantial source of methane to the atmosphere: as much as 50 million metric tons of methane are released per year, in comparison to the 400 million metric tons of carbon dioxide the Arctic stores yearly.
“We don’t understand methane very well, and its releases to the atmosphere are more episodic than the exchanges of carbon dioxide with the atmosphere. It’s important to pay attention to methane dynamics because of methane’s substantial potential to accelerate global warming.”
Exactly how the Arctic system will respond to climate change remains unknown. There are many hypotheses on the subject including ideas that global warming may produce longer growing seasons that promote plant photosynthesis, thus removing carbon dioxide from the atmosphere.
Furthermore, the expansion of shrubs in tundra and the movement of treeline northward could sequester more carbon in vegetation.
McGuire contends that only specific regional studies can determine which areas are likely to experience changes in response to climate change.
“If the response of the arctic carbon cycle to climate change results in substantial net releases of greenhouse gases, this could compromise proposed mitigation efforts for controlling the carbon cycle,” he says.
Editor's note: The article, Sensitivity of the Carbon Cycle in the Arctic to Climate Change, was published in Ecological Monographs. The coordinating lead author is David McGuire, USGS, and the co-authors include internationally renowned scientists from Canada, Germany, Sweden, and the United States. This study was sponsored by the Arctic Monitoring and Assessment Program, the Climate in the Cryosphere Program, and the International Arctic Science Committee.
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